The invention relates to a method for generating a virtual image of vehicle surroundings by using a three-dimensional surroundings model, in particular for use in a vehicle which has a camera surround view system.
Vehicles are increasingly being equipped with driver assistance systems which assist the driver with carrying out driving maneuvers. Said driver assistance systems partially include camera surround view systems which make it possible to display the vehicle surroundings to the driver of the vehicle. Such camera surround view systems comprise one or more vehicle cameras which supply real images of the vehicle surroundings, said real images being combined by a data processing unit of the camera surround view system to produce a surroundings image of the vehicle surroundings. The image of the vehicle surroundings is then displayed to the driver on a display unit.
To this end, the real images of the vehicle surroundings obtained by the cameras of the camera surround view system must first be projected onto projection points of a virtual surroundings model of the vehicle surroundings. The virtual image of the vehicle surroundings thus generated, in turn the image displayed on the display unit can subsequently be calculated from the perspective of a virtual camera. The position of the virtual camera for calculating the displayed image can, in this case, be varied so that depending on the requirements and/or the driving situation, a different representation of the vehicle surroundings can be displayed to the driver. The selection of the three-dimensional surroundings model for projecting the real images and for generating the virtual image is, in this case, crucial for the quality of the displayed image.
To this end, the published patent application DE 10 2012 203 523 A1 discloses a generic method for processing image data of respective images which are captured by multiple cameras positioned on a vehicle, said method involving providing a geometry of a three-dimensional environment model having a planar bottom portion located in a ground plane of the vehicle and a surface which has a bottom surface of the planar bottom portion and which delimits an environment space also including the vehicle. The image data of the respective images of the various cameras are projected as environment model image data onto the surface of this three-dimensional environment model. The image data to be signaled of an image to be signaled from the view of a virtual camera on the surface of the three-dimensional environment model is then determined, based on the fulfillment of a given condition in the sense of a mirror-image representation.
Further generic methods are known from the published patent applications DE 10 2012 219 735 A1 and DE 10 2013 220 005 A1.
Conventional camera-based driver assistance systems therefore project texture information of the camera system onto a static projection surface, preferably onto a three-dimensional shell surface as a surroundings model, wherein the radius of curvature increases as the distance from the vehicle increases, as disclosed for example in the previously indicated DE 10 2013 220 005 A1. In this case, the substantial advantage of a three-dimensional shell surface as a surroundings model compared with a two-dimensional base, i.e. a planar projection surface, is that distortions of raised objects in the vehicle surroundings can be reduced.
However, one substantial disadvantage of the previously used three-dimensional shell-like surroundings models or projection surfaces is that these models are, as a rule, described by means of polar equations or by means of polar coordinates, in particular for the projection algorithm, i.e. in order to realize the projection of the real image data. Such a surroundings model based on polar coordinates is shown, by way of example, in FIG. 1, wherein the points of intersection of the grid model shown in FIG. 1 correspond to the projection points of the surroundings model. As can be seen in FIG. 1, the distance of the projection points from one another also increases as the radial distance from the vehicle increases. The substantial disadvantage of this is that the virtual image of the vehicle surroundings and, therefore also the subsequently displayed image, does not have a constant resolution. Rather, the distance of the sampling points, and therefore in principle the sampling point resolution for the image, increases as the distance from the vehicle increases, which adversely affects the subsequently generated image, e.g. in the form of an intensification of distortion artefacts. The “best” or maximum sampling point resolution, i.e. the smallest distance between the sampling points, is also achieved in a region of the virtual image, for which no real image data at all are available, namely in the region below the vehicle. It is known that no image data are displayed for this region, but a three-dimensional model of the vehicle is usually generated and shown in the displayed image.